It emerged in the report that Mr Alexander confronted Lord Rennard about the allegations “two or three times” but took no further action when he categorically denied them. Ms Morrissey said that reaction was “ultimately not sufficient”.

Scotland Yard has now launched an investigation into the allegations against Lord Rennard, who strongly rejects them and any suggestion of wrongdoing.

In the review, Ms Morrissey said she did not believe there was a cover-up but "mistakes were definitely made".

"They were made by Nick Clegg, Danny Alexander and Jo Swinson," she said.

Paul Burstow, a former minister and chief whip, also admitted a "lapse of judgement" in failing to take further action over complaints made to him by two women.

Mr Clegg said the report made for "sobering reading" and he took responsibility for the failings.

The review reveals that Lord Rennard was spoken to about his behaviour by Mr Alexander in 2008.

Mr Alexander twice raised the matter with Mr Clegg following complaints by two separate groups of women in that year. The allegations were also brought to the attention of Mr Clegg's office once by Jo Swinson, now a business minister.

Mr Clegg's aides initially denied that he knew anything about the allegations, before the party was notified by Channel Four.

A succession of ministers stuck to this line when questioned on television on weekend political programmes.

After several days of denials, Mr Clegg then broke his silence to admit his office had known of "indirect and non-specific claims" against Lord Rennard.

He said at the time: "I am angry and outraged at the suggestion that I would not have acted if these allegations had been put to me. Indeed, when indirect and non-specific concerns about Chris Rennard’s conduct reached my office in 2008, we acted to deal with them.

"My Chief of Staff at the time, Danny Alexander, put these concerns to Chris Rennard and warned him that any such behaviour was wholly unacceptable.

"Chris Rennard categorically denied that he had behaved inappropriately and he continues to do so. He subsequently resigned as Chief Executive on health grounds."

This afternoon, he said the Liberal Democrats made mistakes in their handling of the affair and promised to take on board Ms Morrissey's recommendations.

“It shows that stretching over a 20 year period a series of mistakes were made which left a number of women feeling seriously let down and for that there is absolutely no excuse whatsoever," he said.

“The report also shows that the individuals who dealt with their complaints had the right motives, but there weren’t the right processes in place to support the women who’d come forward.

"And as Leader of the Liberal Democrats I take responsibility for that. That’s why we’ve made a number of big changes in the party in recent years and why we must and will do more."